Prepare Ingredients

1. Preheat Oven: Preheat your oven to 430°F (220°C).
2. Simmer Potatoes: In a saucepan, combine the potato strips with half of the marinade from the sprats, heavy cream, and milk. Simmer gently over medium heat for 10 minutes. This step helps infuse the potatoes with flavor and partially cooks them.
3. Prepare Onions: While the potatoes simmer, thinly slice the onions. In a skillet, melt 2 tablespoons of butter over medium heat and sauté the onions until soft and translucent, about 5-7 minutes.

Assemble the Dish

4. Layer Ingredients: In a large, buttered oven dish (or individual dishes), layer the ingredients in the following order:
   • A layer of the sautéed onions
   • A layer of potatoes
   • A scattering of chopped sprats
   • Repeat layers, ending with potatoes on top.
5. Season: Lightly season each layer with freshly ground black pepper. Use salt sparingly as the sprats or herring may already be salty.

Finish and Bake

6. Add Toppings: Sprinkle the breadcrumbs evenly over the top layer of potatoes. Dot the surface with slices of the remaining butter.
7. Bake: Place the dish in the middle of the oven and bake for 50-60 minutes, or until the top is golden brown and bubbling. If the top browns too quickly, cover loosely with aluminum foil for the last 10-15 minutes of baking.

Serve

8. Allow the dish to cool slightly before serving. Janssons Temptation is perfect as a side dish for festive occasions or as a standalone comfort food.